Wireless tags and readers operating in the high frequency (HF) and the very-high frequency (VHF) systems and/or communicating using magnetic coupling or magnetically coupled transponders (e.g., near field communication [NFC] devices) may suffer performance degradation when placed on or near metal objects due to detuning or reflection of the wireless signal. As a result, relatively poor tag read ranges, phantom reads, and/or no reads occur. For example, NFC and other antennae operating at similar frequencies (˜13 MHz) are effectively unusable if placed on a conductive substrate. However, there is a wide range of uses for devices using these frequencies, such as RF/NFC tags placed on aluminum foil in blister packs.
Conventional solutions to overcome metal detuning for HF and other wireless tags include adding a large spacer or gap between the wireless tag and metal object, or inserting an EMI (electromagnetic interference) shield between the tag and metal object in applications where low profiles are desired. The spacer or gap (e.g., a spacer of non-conducting and/or non-magnetic material) may be positioned between the metal surface and the tag. However, spacers are not often desirable, available or permitted, due to space constraints.
Conventional EMI shields are typically made of ferrite or silicon steel laminate films (50-300 μm). Although conventional ferrite EMI shields may be effective in counteracting the effect of nearby metal objects on tags, conventional ferrite shielding is relatively expensive, especially for relatively large antennas. In addition, conventional ferrite thin films may be brittle, with limited flexibility. Furthermore, conventional ferrite thin films generally cannot be applied to products with small radii (e.g., an AA or AAA battery).
Generally, a conventional EMI silicon steel shield is made of a blanket laminate film having an adhesive backing, which is subsequently applied to the back of an antenna. The EMI shield must be large enough to overlap all traces and/or loops of the antenna for maximum shielding effect. However, when applied to regions that do not need to be shielded, using a conventional EMI silicon steel shield with a blanket laminate film may waste raw silicon steel shield material, which typically makes up the largest portion of the total shield cost.
As a practical matter, the raw material for shielding is limited, as low cost solutions (approximately a few cents) must be used for fabricating wireless tags and devices that can be read on metal surfaces. Furthermore, patterning or cutting conventionally available EMI laminate films is not practical or cost effective, as the removed material is not easy to recycle or recover cost-effectively. Consequently, conventional EMI films may be too costly to be accepted widely for wireless (e.g., NFC and RF) tags for inexpensive products. In addition, conventional EMI films may have physical and/or structural limitations, due to their brittleness and limited flexibility.
Since conventional EMI films (e.g., ferrite shields) generally add cost to the tags and/or products to which the tags are attached, and can introduce implementation issues in some cases, a low cost solution to counteract and/or mitigate the effect of metal on or in proximity to magnetically coupled near field communication devices is desired.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.